Enhancement of coral recruitment by in situ mass culture of coral larvae
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Published source details
Heyward A. J., Smith L. D., Rees M. & Field S. N. (2002) Enhancement of coral recruitment by in situ mass culture of coral larvae. Marine Ecology Progress Series, 230, 113-118.
Published source details Heyward A. J., Smith L. D., Rees M. & Field S. N. (2002) Enhancement of coral recruitment by in situ mass culture of coral larvae. Marine Ecology Progress Series, 230, 113-118.
Summary
Natural coral recruitment at Coral Bay (Western Australia) is very low, but multi-species aggregations of coral embryos frequently form slicks on the sea surface after large-scale annual spawnings. Spawning events are often fairly predictable for a given location; the slicks contain billions of gametes and embryos, many of which are normally lost but which provide a potential source of coral recruits, if a mechanism can be developed for capturing, culturing and seeding them. This experiment looked at the possibility of enhancement of coral recruitment by in situ mass culture of coral larvae derived from such spawning events.
Initial collection: At Coral Bay, four floating pools were constructed and moored over the reef, a few hundred metres from shore. Each pool was approximately 1.8 m diameter, made of nylon-reinforced vinyl fabric and held in a PVC raft frame at the waters surface by car tyre inner tubes positioned under each corner. In March 1997, most of the acroporids in Coral Bay spawned between 21:15 and 22:30 h. Samples were collected from the surface of the slick in buckets and placed in the pools (c.1 million/pool). An estimated 4 million coral embryos of 18 species were collected.
Coral seeding: Six days later, 80% of the embryos were ready to settle. Each pool was towed behind a small boat to one of four reef areas within the Bay; the larvae within them were mixed during the journey by the agitation caused by wind and waves. At the chosen seeding sites, the mesh windows in the pool walls were covered and bilge pumps turned on causing the water to rise inside, which resulted in the larvae being flushed down a plastic hose inserted into the base of the pool. The hose was connected to the roof of a floorless, mesh tent (1.8 x 1 m, 200 μm mesh) placed on the reef substrate to retain the larvae.
Monitoring: Recruitment density was monitored using (110 x 110 x 10 mm thick) terracotta tiles attached to the substrate at treatment and randomly distributed control (no seeding) sites. The tiles had been placed in the water 3 weeks earlier to allow formation of a biofilm. Six weeks after seeding, the tiles were removed and examined under a stereo microscope. Each coral recruit (dead or alive) was identified to one of four groups (Acroporidae, Pocilloporidae, Poritidae or Other) and the surface that they settled on the tile (upper, lower or horizontal) was recorded.
Recruitment was much higher at the seeded sites: a total of 6,539 coral recruits were counted. Coral larvae settled on all surfaces of the tiles with the majority on the lower horizontal surfaces (60%). Only 18 recruits were brooding species (all pocilloporids); the vast majority were broadcast-spawning corals (all acroporids). Recruitment in the most highly seeded areas was 100 times more (236 recruits/tile) than the natural levels of recruitment in Coral Bay (0.27 recruits/tile).
This study shows that mass rearing of coral larvae using a simple system is feasible, and can be used to increase natural coral recruitment, albeit at small scales.
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